1. Field of the Invention
The present invention relates to a liquid ejection head, an image forming apparatus and a method of manufacturing a liquid ejection head, and more particularly, to a liquid ejection head, an image forming apparatus and a method of manufacturing the liquid ejection head, which liquid ejection head has excellent ejection performance, as well as being suitable for mass production and cost reduction.
2. Description of the Related Art
There are commonly used liquid ejection heads which include nozzles, pressure chambers connected to the nozzles, and actuators that change the pressure inside the pressure chambers, liquid being ejected from the corresponding nozzle when a drive signal is applied to the actuator. In liquid ejection heads which use piezoelectric actuators as actuators, in general, a piezoelectric body and an electrode are formed on a diaphragm that constitutes one side wall of each pressure chamber, and the pressure of the pressure chamber is changed through the diaphragm.
In these liquid ejection heads, similarly to when manufacturing semiconductor devices, a circular disk-shaped wafer made of monocrystalline silicon (silicon substrate) is prepared, and a diaphragm, piezoelectric bodies and electrodes are formed on this silicon substrate.
For example, Japanese Patent Application Publication No. 4-312852 discloses a head in which a diaphragm made of a silica film is formed on the surface of the silicon substrate by means of a thermal oxidation process.
Japanese Patent Application Publication No. 2004-209874 discloses a head in which a diaphragm made of pyrex glass is bonded to a silicon substrate, and the diaphragm is etched from the pressure chamber side to form smooth, edge-free recess sections in the diaphragm.
If liquid ejection heads are manufactured by using a circular disk-shaped wafer made of monocrystalline silicon (silicon substrate), then the number of liquid ejection heads that can be manufactured from one wafer is limited by the surface area of the disk-shaped wafer, and hence there are limitations on the mass production of liquid ejection heads and the reductions that can be achieved in the related manufacturing costs. In this respect, if it were possible to increase the surface area of the base material, for instance, by using a substrate material that can be supplied in the form of a roll, then this would be beneficial from the viewpoint of achieving mass production of liquid ejection heads and reducing manufacturing costs.
On the other hand, there have also been demands to arrange nozzles at high density. With increase in the nozzle density, it is necessary to reduce the size of the pressure chambers and to reduce the thickness of the film forming the diaphragm, but at the same time, any decline in the ejection performance must be prevented. For example, when it is sought to form an image on an ejection receiving medium by ejecting ink from a liquid ejection head, then even if the image resolution can be raised by increasing the density of the nozzles, for example, if ejection is not performed correctly, or if there are variations in ejection between different nozzles, then the quality of the image is decline. Moreover, if the ejection efficiency per nozzle is poor, then the liquid ejection head as a whole consumes a large amount of energy corresponding to the number of nozzles. Furthermore, if the production yield is poor, then it is not possible to reduce manufacturing costs.
In a bending type of actuator that uses a bimorph element, the characteristics of the diaphragm govern the characteristics of the actuator, and it is necessary to achieve a thinner diaphragm (having a thickness of 10 μm or less, for example), especially if the density of the nozzles is increased.